The Apostle John was given revelation that pertains to the 20th and 21st century. The account in Revelation 17 depicts the number of popes ruling the Vatican in the last century. We are told how many there will be as the fall of each pope brings us closer to the beast. As we will soon see, the successor to the current pope is the false prophet.
Revelation 17:9-11
"This calls for a mind with wisdom. The seven heads are seven hills on which the woman sits.
They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for a little while.
The beast who once was, and now is not, is an eighth king. He belongs to the seven and is going to his destruction."
Seven hills in verse 9 is the city of Rome (see: http://en.wikipedia.org/wiki/Seven_hills_of_Rome ).
The woman in verse 9 is a church, as the scriptures are consistent to depict churches as a woman, virgin maiden, harlot, or bride.
So the woman who sits in the seven hills is a direct reference to the Roman Catholic Church. You might be asking how it is that the next passage talks about there being kings. Does the Roman Catholic Church have any "kings" or just popes?
The answer to this question is that the Vatican has kings since 1929, when the Vatican was recognized as an independent sovereign nation no longer part of Italy. From 1929 until today, each reigning pope is also the king of the Vatican state. So, lets count and name each king from 1929 until today and see how many we count.
Verse ten refers to the current king/pope - Benedict XVI. It is revealed that he will be king for a short while. It is interesting to note that a recent controversy has many bishops calling for the resignation of Benedict XVI. You can read about it here: http://www.spiegel.de/international/world/0,1518,605714,00.html
In short, the Vatican reinstated a parishioner who denies the holocaust, and the outrage over this has many speculating that Benedict will tender his resignation.
Who will follow the current pope? We do not know who it will be, but we know what will happen when the beast takes the helm over the woman who sits in the seven hills. The timing of the shift of power to the next guy will shortly precede with the timing of going into destruction - the seven year great tribulation.
Woe to those on His left on that Day. They will be cast into the fire. ~ God [Letters from God and His Christ - Volume 1 - Those Whom the Lord Has Cleansed Are Now Clean Now Now, and Worthy of the Kingdom]